You are right. The radius decreases. But we can figures out the why for both parts by the following:
Think about this. Let's pick the first element in the period (Na) and the last element in the period (Cl).
Na has 11 protons (+ charge) in the nucleus. Cl has 17 + charges in the nucleus. Which will pull harder on trying to get those electrons (remember + charges attract negative charges) to come in with them. Of course, the 17+ charges will pull harder; therefore, the Cl is smaller than the Na.
Now for ionization potential.
If we are trying to pull the outside electron away, which will be harder? To pull an electron (with a negative charge) away from 11+ charges or to pull an electron away from 17+ charges. Of course it will be harder to pull an electron away from 17+ charges won't it. So the ionization potential generall increases as we go from left to right.